The use of ball grid arrays (BGAS) to package electronic circuits and devices such as integrated circuit chips is becoming more prevalent. BGA packaging has proven to provide substantial advantages over other packaging techniques such as, for example, dual in-line packages (DIPs), pin grid array (PGA) packages, tape carrier packages (TCPs), and quad flat packs (QFPs). The advantages of BGA packaging become especially significant when used to package an integrated circuit chip or die having a high pin count and when used to package devices employing high frequency signals. BGA packaging provides the additional advantage of being able to use conventional surface mount technologies (SMTs) and assembly techniques when mounting to a printed circuit board (PCB).
A BGA package generally includes a die or chip, one or more substrate layers provided on top of one another and aligned through a cavity portion, an array of solder balls for providing an electrical and mechanical connection external to the BGA package, and a heat spreader/stiffener for providing a thermal conduction path to cool the die and to provide mechanical support and rigidity to the BGA package. The substrate layers include metal layers and traces that serve as signal and/or power distribution connections in addition to distinct power and ground planes.
Each of the solder balls of the array of solder balls is positioned on an exposed substrate and electrically coupled to either a ground pad, a power pad, or a signal pad provided by the various substrate layers. Some of the solder balls may also couple to sacrificial pads that are provided for mechanical advantages and do not provide an electrical connection to the package. The electrical connections are generally made through vias or metallized interconnections provided through the various substrate layers. The fabrication of the vias and substrate layers is expensive, time consuming, and reduces the overall packaging yield and reliability of high pin-count packages.
A die is generally mounted on the heat spreader/stiffener using an adhesive or glue such as an epoxy. The die bond pads are electrically coupled to the various solder balls of the array of solder balls by directly coupling the die bond pads to either the ground plane, the power plane, or to a corresponding signal trace of one of the substrate layers. The connection is generally provided using wire bonding techniques. These connections are expensive and complicated by the fact that connections must be made with multiple substrate layers.
The fabrication of the substrate layers, metal layers, and traces is expensive. In general, multiple substrate layers and multiple vias result in lower BGA package fabrication yields and higher costs. The formation of the vias create additional complexity and cost because each of the vias generally require the formation of a conductive layer, such as a metal layer on the internal walls of the via, to ensure a complete electrical path. This may be referred to as metallization. The metallization of the internal walls of each via increases the overall complexity and cost of manufacturing multiple substrate layer BGA packages.